Effects of film thickness and thermal treatment on the structural and opto-electronic properties of Ga-doped ZnO films deposited by sol–gel method

• Novel 1 at% Ga doped ZnO thin films prepared by the sol gel method.
• Film thickness, heating temperature and atmosphere dependent film properties observed.
• High visible transmission (with an average value of 80–90%) obtainable.
• The relationship between electrical parameters and thermal emissivity firstly discussed.

In this work, Ga-doped ZnO (GZO) films were prepared using the sol–gel dip coating method and the effects of film thickness (230–480 nm), heating temperature (400–600 °C) and atmosphere (air/argon) on the system structural and opto-electronic performances were investigated. The results show that highly c-axis oriented crystals could be easily formed in GZO coatings, which origins from a preferred nucleation and gets fully developed during the structure evolution. The increase of film thickness prolongs the sol–gel preheating process and promotes nucleation, resulting in a more crystalline film. Higher temperature annealing (600 °C) in air could degrade the Ga doping efficiency and decrease the carrier concentration, but the enlarged grain size helps enhance the carrier mobility and improve the film conductivity. Under the modified annealing process in argon, favorable carrier density (3.376×1019 cm−3) and mobility (15.74 cm2(V s)−1) can be obtained at the same time, resulting a minimum film resistivity of 1.18×10−2 Ω cm. The studied GZO coatings keep transparent in the visible and near infrared range, leading to high emissivity values (>0.738). We firstly prove that the carrier concentration could play a more dominant role than its mobility in determining the thermal emittance performance of thin films.